1. Field of the Invention
The present invention relates to a motor control device and a control method of a stepping motor, and particularly, to a motor control device and a control method of a stepping motor which measure a back electromotive voltage to detect out-of-step.
2. Description of the Related Art
A stepping motor has various features, for example, the stepping motor is easily controlled, and is widely used for various actuators, and the like. The stepping motor includes a stator and a rotor which have no contact with each other, and thus has a long life. Also, large static torque is obtained when the stepping motor is in an excited state.
In the stepping motor, so-called out-of-step may occur, and occurrence of out-of-step may cause a problem. If the stepping motor becomes out of step, the rotor may not normally rotate, resulting in the uncontrollable state. Out-of-step may be caused by loss of synchronization between an input pulse signal and rotation of a motor, for example, when an excessive load greater than a driving torque of the motor is applied or when a rapid speed change occurs.
In general, the stepping motor is used for controlling an angle and speed of rotation with a high degree of accuracy. Since the stepping motor manages its rotational position according to the number of pulses oscillated from a control side, if detection of out-of-step is delayed and only control proceeds, a driving object such as a position of a gear may deviate. Also, if detection of out-of-step is delayed, acoustic noise may be caused. Therefore, in order to perform an appropriate operation in the actuator or the like using the stepping motor, it is required to quickly detect occurrence of out-of-step.
That is, when the stepping motor becomes out of step, it is necessary to quickly detect out-of-step, and quickly perform error processing such as stopping rotation or returning to a normal rotation state. Therefore, in the stepping motor, a circuit or a system for detecting out-of-step and then performing error processing is often used.
Incidentally, the following technique related to an apparatuses using a stepping motor has been disclosed. JP-A-2007-215271 discloses a technique for performing control so as to prevent superfluous driving pulse signals from being fed into a stepping motor in an initialization operation when driving of the stepping motor is controlled without using a rotational position sensor or the like. That is, when the initialization operation is performed, the stepping motor is driven in a predetermined rotation direction, and an induced voltage generated between winding wires of non-excitation phases is compared with a predetermined reference voltage, whereby a rotation state of the motor is detected. If it is detected that the motor is locked, control is performed such that the motor rotates reversely by a predetermined number of pluses based on a predetermined driving pulse signal.
JP-A-2002-199794 discloses a technique for rotating a stepping motor used in a recorder reversely if out-of-step is detected, as a method of restoring rotation of the motor when out-of-step of the motor is detected.
This process is performed for grasping a leading end of a paper sheet missed due to the out-of-step. Further, JP-A-2002-199794 also discloses a technique for rotating the motor while gradually reducing the rotation speed to prevent out-of-step when performing forward rotation after the reverse rotation.